1 files changed, 143 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/snapshot_map/mod.rs b/compiler/rustc_data_structures/src/snapshot_map/mod.rs
new file mode 100644
index 000000000..8a50179cd
--- /dev/null
+++ b/compiler/rustc_data_structures/src/snapshot_map/mod.rs
@@ -0,0 +1,143 @@
+use crate::fx::FxHashMap;
+use crate::undo_log::{Rollback, Snapshots, UndoLogs, VecLog};
+use std::borrow::{Borrow, BorrowMut};
+use std::hash::Hash;
+use std::marker::PhantomData;
+use std::ops;
+
+pub use crate::undo_log::Snapshot;
+
+#[cfg(test)]
+mod tests;
+
+pub type SnapshotMapStorage<K, V> = SnapshotMap<K, V, FxHashMap<K, V>, ()>;
+pub type SnapshotMapRef<'a, K, V, L> = SnapshotMap<K, V, &'a mut FxHashMap<K, V>, &'a mut L>;
+
+#[derive(Clone)]
+pub struct SnapshotMap<K, V, M = FxHashMap<K, V>, L = VecLog<UndoLog<K, V>>> {
+    map: M,
+    undo_log: L,
+    _marker: PhantomData<(K, V)>,
+}
+
+// HACK(eddyb) manual impl avoids `Default` bounds on `K` and `V`.
+impl<K, V, M, L> Default for SnapshotMap<K, V, M, L>
+where
+    M: Default,
+    L: Default,
+{
+    fn default() -> Self {
+        SnapshotMap { map: Default::default(), undo_log: Default::default(), _marker: PhantomData }
+    }
+}
+
+#[derive(Clone)]
+pub enum UndoLog<K, V> {
+    Inserted(K),
+    Overwrite(K, V),
+    Purged,
+}
+
+impl<K, V, M, L> SnapshotMap<K, V, M, L> {
+    #[inline]
+    pub fn with_log<L2>(&mut self, undo_log: L2) -> SnapshotMap<K, V, &mut M, L2> {
+        SnapshotMap { map: &mut self.map, undo_log, _marker: PhantomData }
+    }
+}
+
+impl<K, V, M, L> SnapshotMap<K, V, M, L>
+where
+    K: Hash + Clone + Eq,
+    M: BorrowMut<FxHashMap<K, V>> + Borrow<FxHashMap<K, V>>,
+    L: UndoLogs<UndoLog<K, V>>,
+{
+    pub fn clear(&mut self) {
+        self.map.borrow_mut().clear();
+        self.undo_log.clear();
+    }
+
+    pub fn insert(&mut self, key: K, value: V) -> bool {
+        match self.map.borrow_mut().insert(key.clone(), value) {
+            None => {
+                self.undo_log.push(UndoLog::Inserted(key));
+                true
+            }
+            Some(old_value) => {
+                self.undo_log.push(UndoLog::Overwrite(key, old_value));
+                false
+            }
+        }
+    }
+
+    pub fn remove(&mut self, key: K) -> bool {
+        match self.map.borrow_mut().remove(&key) {
+            Some(old_value) => {
+                self.undo_log.push(UndoLog::Overwrite(key, old_value));
+                true
+            }
+            None => false,
+        }
+    }
+
+    pub fn get(&self, key: &K) -> Option<&V> {
+        self.map.borrow().get(key)
+    }
+}
+
+impl<K, V> SnapshotMap<K, V>
+where
+    K: Hash + Clone + Eq,
+{
+    pub fn snapshot(&mut self) -> Snapshot {
+        self.undo_log.start_snapshot()
+    }
+
+    pub fn commit(&mut self, snapshot: Snapshot) {
+        self.undo_log.commit(snapshot)
+    }
+
+    pub fn rollback_to(&mut self, snapshot: Snapshot) {
+        let map = &mut self.map;
+        self.undo_log.rollback_to(|| map, snapshot)
+    }
+}
+
+impl<'k, K, V, M, L> ops::Index<&'k K> for SnapshotMap<K, V, M, L>
+where
+    K: Hash + Clone + Eq,
+    M: Borrow<FxHashMap<K, V>>,
+{
+    type Output = V;
+    fn index(&self, key: &'k K) -> &V {
+        &self.map.borrow()[key]
+    }
+}
+
+impl<K, V, M, L> Rollback<UndoLog<K, V>> for SnapshotMap<K, V, M, L>
+where
+    K: Eq + Hash,
+    M: Rollback<UndoLog<K, V>>,
+{
+    fn reverse(&mut self, undo: UndoLog<K, V>) {
+        self.map.reverse(undo)
+    }
+}
+
+impl<K, V> Rollback<UndoLog<K, V>> for FxHashMap<K, V>
+where
+    K: Eq + Hash,
+{
+    fn reverse(&mut self, undo: UndoLog<K, V>) {
+        match undo {
+            UndoLog::Inserted(key) => {
+                self.remove(&key);
+            }
+
+            UndoLog::Overwrite(key, old_value) => {
+                self.insert(key, old_value);
+            }
+
+            UndoLog::Purged => {}
+        }
+    }
+}